| Optivision Opticians Limited | Health & social care | 2005 |
| Optix Eyecare Ltd | Health & social care | 2024 |
| Optom Cover Ltd | Health & social care | 2024 |
| Optomedic Ltd | Health & social care | 2015 |
| Optometry Wellness Ltd | Education | 2021 |
| Optomline Ltd | Wholesale & retail | 2023 |
| Optopharm Ltd | Health & social care | 2006 |
| Optowork Ltd | Administrative & support | 2025 |
| Optyco Limited | Health & social care | 2012 |
| OPU Accessories Ltd | Wholesale & retail | 2023 |
| OPU Jewels Ltd | Wholesale & retail | 2021 |
| Opulensi Ltd | Wholesale & retail | 2023 |
| Opulent 4 Homes Ltd | Real estate | 2025 |
| Opulent Cleaning Ltd | Administrative & support | 2025 |
| Opulent Curtains & Blinds Limited | Manufacturing | 2023 |
| Opulent Residential Family Support Services Ltd. | Health & social care | 2025 |
| Opulent Retreats Ltd | Hospitality | 2025 |
| Opulent Sales Ltd | Wholesale & retail | 2023 |
| Opulent Touches Ltd | Construction | 2022 |
| Opulento Ltd | Financial services | 2022 |
| Opulora Ltd | Professional & scientific | 2024 |
| Opus 107 Limited | Administrative & support | 2014 |
| Opus Installations Limited | Construction | 2007 |
| Opus Trust Communications Limited | Extraterritorial | 2019 |
| Opus Trust Marketing Limited | Manufacturing | 1999 |
| Opuspond Limited | Information & communication | 2014 |
| Oqtagon Atelier Limited | Wholesale & retail | 2026 |
| Orabelle Group Limited | Wholesale & retail | 2025 |
| Oracare Hygiene Ltd | Health & social care | 2024 |
| Oracle LED Lighting Ltd | Construction | 2017 |
| Oral and Maxillofacial Surgical Services Ltd | Health & social care | 2011 |
| Oram (Leicester) Limited | Financial services | 2015 |
| Orana Fashions Limited | Manufacturing | 2020 |
| Orana General Trading Ltd | Wholesale & retail | 2025 |
| Orange FOX Studios Limited | Information & communication | 2016 |
| Orange Genie Admin PAY Ltd | Administrative & support | 2017 |
| Orange Genie PAY NO 2 Ltd | Administrative & support | 2011 |
| Orange House Properties Limited | Construction | 2021 |
| Orange Reel Productions Ltd | Information & communication | 2012 |
| Orange Sofa Lettings Ltd | Real estate | 2025 |
| ORB Dynamics Ltd | Professional & scientific | 2020 |
| ORB Trading Ltd | Manufacturing | 2023 |
| Orb-One Ltd | Manufacturing | 2025 |
| Orbella Ltd | Manufacturing | 2026 |
| Orbit Mobiles Syston Limited | Manufacturing | 2024 |
| Orbit Property Ventures Limited | Real estate | 2026 |
| Orbital Innovation Ltd | Professional & scientific | 2024 |
| Orbital Supply Limited | Wholesale & retail | 2026 |
| Orbital Systems UK Ltd | Professional & scientific | 2023 |
| Orbitz Ihomes Ltd | Health & social care | 2025 |
| Orbitz Logistica(Uk) Ltd | Wholesale & retail | 2024 |
| Orca CT Trading Limited | Wholesale & retail | 2016 |
| Orca&Co Ltd | Wholesale & retail | 2024 |
| Orchard Business Partners Ltd | Information & communication | 2016 |
| Orchard Court Leicester Limited | Health & social care | 2018 |
| Orchard END Consultancy Services Ltd | Professional & scientific | 2017 |
| Orchard Engineering Ltd | Manufacturing | 2015 |
| Orchard Green Projects Ltd | Construction | 2017 |
| Orchard Hall Estates Limited | Real estate | 2017 |
| Orchard House (Leicester) Management Company Limited | Households | 2001 |
| Orchard Housewares Limited | Wholesale & retail | 2023 |
| Orchard Manor View Limited | Health & social care | 2014 |
| Orchard Mews (Blaby) Management Company Limited | Households | 2010 |
| Orchard Residences Ltd | Real estate | 2022 |
| Orchestrate Health Services Limited | Health & social care | 2021 |
| Orchid House Serviced Apartments Ltd | Hospitality | 2018 |
| Ordesa Limited | Professional & scientific | 2022 |
| Oregano Leaf (Wood Fire) Ltd | Hospitality | 2019 |
| Oreon Corporation LP | | 2017 |
| Organic Land Global Ltd | Wholesale & retail | 2017 |
| Organic Salts Ltd | Wholesale & retail | 2024 |
| Organicbio Ltd | Manufacturing | 2022 |
| Organicoo Ltd | Wholesale & retail | 2023 |
| Organikon Limited | Professional & scientific | 2014 |
| Organization for Recorded Culture and Arts Ltd | Information & communication | 2025 |
| Organized Kaos Ltd | Manufacturing | 2024 |
| Orgesto Zdrava Limited | Construction | 2025 |
| Orient UK Group Ltd | Administrative & support | 2024 |
| Oriental Cherry Limited | Hospitality | 2021 |
| Oriental House Duan Ltd | Hospitality | 2025 |
| Oriental House Ming Ltd | Hospitality | 2019 |
| Oriental Therapy Centre Ltd | Other services | 2026 |
| Oriental Therapy Ltd | Other services | 2018 |
| Origin Fashions Ltd | Manufacturing | 2019 |
| Origin Holdings 2019 Ltd | Financial services | 2019 |
| Original Graphics Ltd | Professional & scientific | 2020 |
| Original Ideas Limited | Other services | 2020 |
| Original Oasis Bar Limited | Hospitality | 2020 |
| Orion Electrical Contractors Ltd | Construction | 2012 |
| Orion Offshore Limited | Real estate | 2002 |
| Orion P.I.C Ltd | Real estate | 2025 |
| Orion PCN Ltd | Health & social care | 2022 |
| Orka Studios Limited | Wholesale & retail | 2020 |
| Orlahrose Properties Limited | Real estate | 2025 |
| Orleis Ltd | Manufacturing | 2025 |
| Orluck Ltd | Real estate | 2019 |
| Ormhm Ltd | Financial services | 2026 |
| ORO Kitchen Ltd | Hospitality | 2025 |
| ORO Wellbeing Ltd | Wholesale & retail | 2022 |
| Orodent Ltd | Health & social care | 2007 |